1. Field of the Invention
The present invention relates to a method and apparatus for simultaneously measuring the dielectric and thermal properties of a material. The present invention also relates to a specialized sample cell for performing these measurements.
2. Discussion of the Related Art
Thermoset polymers represent a very important class of materials for many types of manufacturing, including automotive. In automotive production, thermoset resins are used as induction- or oven-curable adhesives, reactive sealants, paints and primers, packaging and encapsulation resins for electric and electronic devices, structural composite components, composite body panels, etc. Thermoset materials, once properly cured, provide superior dimensional stability due to the chemical crosslinks in their molecular structure. Since the extent of cure of the crosslinked polymers is one of the most important factors in governing the performance of the final products, the cure of thermoset materials have been studied extensively by both theoretical and experimental means. Dielectric measurements have been applied to the studies of curing of thermoset materials because such measurements can be carried out through the curing cycle from liquid resin to highly crosslinked solid. Recent technological developments in micro-electronics have made silicon-chip based interdigitated comb electrodes available for microdielectrometry. Microdielectrometry provides a sensitive and convenient way of measuring molecular and ionic mobility in liquid resins or solid polymers. It is known that the progress of curing reaction of thermoset resins can be monitored by microdielectrometry. Microdielectrometry, however, provides only a relative measure of cure of a given commercial resin. An absolute characterization of cure requires the use of additional experimental methods which have previously been performed at a different time.
Differential Scanning Calorimetry (DSC) provides quantitative measurements of the instantaneous heat capacities and thermal events of polymer liquids or solids. Thus, DSC is an ideal method for quantifying the amount of heat being released during the highly exothermic polymerization reactions of thermoset polymers. DSC has also been applied to study quantitatively the cure kinetics of thermoset resins. The extent of curing reaction can be readily calculated by normalizing the amount of heat released from a reacting resin at a given condition to the total heat of reaction. The temperature control in a DSC chamber is superior to that of many programmable ovens, and thus, precisely controlled cure schedules can be achieved. DSC, however, does not allow in-situ measurement of cure for industrial applications. Furthermore, DSC cannot measure diffusion process of thermoplastic plastisols commonly used as a component in industrial adhesives and sealers.